The use of electronic cameras to capture still image data for subsequent transmission and display has become increasingly popular in applications where time is of the essence. Electronic imaging systems presently have lower resolution capabilities than conventional silver halide photographic systems, but the ability to quickly transmit and manipulate electronic image data offsets the resolution disadvantage when time is a critical factor. Many news gathering organizations, for example, now take advantage of electronic camera systems that permit a photographer to image a scene at a remote location and transmit the captured image data directly to central offices for review, editing and subsequent printing.
Electronic imaging systems, however, have another disadvantage when compared with silver halide photography systems, namely, electronic imaging systems generally have a much lower exposure latitude than conventional silver halide systems. Thus, exposure control in electronic imaging systems is of critical importance for producing acceptable images. For example, the best CCD camera images are usually obtained when the maximum exposure is employed which does not overexpose, thereby saturating the pixel elements of the CCD camera, or underexpose the objects of interest in the scene to be captured. It is possible to devise exposure control algorithms to automatically control the exposure operation in electronic imaging systems to accomplish optimum exposure control under given scene illumination conditions. A general algorithm that is capable of providing optimal exposure control for a wide variety of exposure conditions, however, is extremely difficult to generate as optimal exposure conditions are very scene dependent.
It would therefore be desirable to provide an apparatus capable of providing feedback to the user of an electronic camera system when optimal exposure conditions have been reached for any given scene. It would further be desirable to provide a "feedback" apparatus of simple and inexpensive design that could be readily incorporated into conventional electronic imaging systems.